Arch shape cross section storm chambers made from injection molded plastics have been used for a number of years to handle stormwater. In a typical installation, multiple rows of strings of interconnected chambers are placed on the floor of a cavity made in the earth surface and are then backfilled with crushed stone or the like. Stormwater, such as might run-off from a paved parking lot or roofs of buildings is channeled to the chambers so the waters can accumulate and then be dispersed over time by either percolation into the surrounding soil or by controllably flowing to a water course.
Some types of arch shape cross section chambers, exemplified by a corrugated chamber described in Detullio U.S. Pat. No. 5,087,151, have closed ends and are interconnected by pipes. Those chambers might be made by thermoforming of thermoplastic sheet. Another type of chamber, of more relevance to the invention described herein, is exemplified by the chambers shown in Kruger U.S. Pat. No. 7,118,306. Those kinds of chambers are preferably made by injection molding. The chambers have open ends. A string of chambers is assembled by overlapping a first end of one chamber on the second end of a like chamber, when the like chamber has been previously placed within a cavity in the earth. After installation, the chambers are backfilled, typically with crushed stone, and the stone is covered to create a soil surface, often a paved surface which can be used by motor vehicles.
When so installed beneath the surface of the earth, stormwater chambers should have requisite strength and durability, particularly for bearing the overlying load of soil and any vehicular or other traffic.
Systems comprised of molded plastic arch shape cross section stormwater chambers are in functional- and cost-competition with other stormwater systems, including buried systems comprised of steel conduit and detention ponds. Generally, it is an objective to have storm chambers with larger and larger volumetric capacity per unit length, while of course still meeting the load bearing requirements. Whereas early plastic chambers used 20 years or more ago had a peak height of 12 inches, more recent chambers may be quite large. For example, a commercial Model 4500 stormwater chamber sold by Stormtech LLC, Rocky Hill, Conn. is 100 inches wide at the base, about 60 inches high, about 48 inches long, and weighs about 120 pounds. There is a generalized desire to commercialize even larger chambers.
There are practical problems encountered with large chambers. Among them are: First, it is not easy to mold large chambers because they require large molding machines and machinery for handling the just-molded products. Large and thus less common injection molding machines can be costly.
Second, large chambers present problems with respect to storing and shipping in economic fashion by truck —the most common mode. Typically chambers are nested one within the other to form a stack for shipment on pallet. But the basic height of a chamber is large to begin with, then that means not many chambers can be nested before the height capacity of a ordinary highway truck is exceeded. For example, if the load height capacity of a truck is about 100 inches from the bed surface, and one chamber is 60 inches high, then there is only an about 40 inches of space for containing nested chambers. If the stack height is about 6 inches (the spacing between one chamber and next-nested chamber), then only 6-7 chambers can be stacked on top of the bottom chamber.
Third, the weight of each individual chamber can exceed that which workers can handle manually, particularly at the site where the stormwater system is being constructed, necessitating the use of materials handling equipment. It is more convenient for installers to not have to use lifting devices.